1. Field of the Invention
The present invention concerns a method for determination with a magnetic resonance system of the position and/or orientation of the image plane of slice image exposures of a vessel region in a contrast agent bolus examination, in particular in the region of the aorta bifurcation or the aorta arch, wherein the image plane traverses the vessel region in the longitudinal section, and wherein a group of slice image exposures lying essentially orthogonal to the vessel is acquired from different planes of the vessel region.
2. Description of the Prior Art
A contrast agent bolus examination, frequently also called CareBolus measurement, serves for the determination of the flow-through time of the contrast agent in the framework of a magnetic resonance examination, for example in peripheral angiography. For an angiographic examination, the injection of a contrast agent is necessary in order to be able to depict very fine vessel structures in the acquired image. Problematic in these examinations is the determination of the start time for the actual angiography scan (imaging). This must be started when the contrast agent is present in sufficient concentration in the vessel or vessels of the respective body region to be examined. Otherwise it is not possible to acquire sufficiently high-contrast images, for example subtraction images. In order to be able to determine the correct point in time, CareBolus examination is implemented, in which a vessel region through which the contrast agent bolus proceeds is monitored via the magnetic resonance system. The point in time of the entrance of the contrast agent bolus into the slice image is used as a basis for the triggering of the subsequent angiography imaging.
In order to be able to detect the contrast agent bolus in a particular vessel region, for example, the region of the aorta bifurcation or the aorta arch, the region in question is monitored by magnetic resonance imaging. The image plane of the monitoring slice image is placed in the longitudinal direction proceeding through the vessel region in order to be able to monitor a certain vessel length and to be able to detect the incidence of the bolus in every case. In order to determine the slice plane, conventionally a number of slice images proceeding transversely to the vessel longitudinal axis are acquired using the magnetic resonance system. These slice Images are shown to the physician on a monitor and are evaluated by the physician with regard to the actual spatial course of the vessel region, and using this evaluation the position and/or orientation of the slice image plane is determined for the actual contrast agent bolus monitoring. The position/orientation of the plane depends on the position of the vessel region in the body of the patient with regard to the coordinate system of the magnetic resonance system.
Because the contrast agent bolus migrates relatively quickly, the bolus measurement is accorded central importance for the subsequent angiography examination. In the framework of the bolus monitoring, a decisive criterion is that the image plane of the bolus slice images be optimally positioned in order to be able to determine the arrival of the bolus as early as possible. This is even more critical in a magnetic resonance examination because the contrast agent generally can be administered only a single time in order to obtain high-contrast subtraction images. An injected contrast agent is not reabsorbed by the patient until hours later, during which another administration of contrast agent is not feasible.
German OS 102 21 642 discloses a method for slice tracking in the acquisition of images of time-dependent moving structures that enables a phase-dependent slice planning for triggered measurements based on slice position markings that are set manually by the operator. For this purpose, initially a number of time-dependent reference images are acquired that all lie in the same plane. In these reference images that show the examination region, dependent on its movement, in different positions, slice position markings are manually indicated by the physician that define the position of the image plane in which a slice image is subsequently to be acquired at the same point in time as the reference image. The relevant acquisition points in time of the respective reference image are automatically associated with the individual slice position markings as time markers.
From German OS 199 43 404, a method is known in which automatic overview images are acquired within which anatomical landmarks are identified. A determination subsequently ensues of the suitable measurement parameters for later image acquisition using previously acquired, stored overview images in the framework of a correlation. For this, a corresponding transformation of the currently acquired images ensues by displacement, rotation, stretching, compression, etc., with the transformation that has the best correlation coefficients being used for adaptation of the parameter to the measurement sequence.
U.S. Pat. No. 6,195,409 discloses a method in which structure information with regard to a subject shown in the image is acquired using a localizer image, with the determined structures correlated with corresponding comparison images, for which a rotation, displacement or the like is effected in order to find the best-coinciding correlation image. Using the image plane in which the best-coinciding correlation image was acquired, the corresponding image planes of the subsequent subject to be acquired are subsequently determined, which is accomplished using known transformation parameters that have been determined in the framework of the correlation.
German OS 195 29 636 also describes a method for spinal acquisitions, in the framework of which initially a sagittal overview image of the spinal column is acquired and shown to the physician on a monitor. The physician now designates lines in the representation that proceed through the individual intervertabral discs and that determine the image planes that should be subsequently acquired. This ensues manually via a computer mouse, etc. Once the slices are determined, the necessary subject volume is determined and subsequently the 3D date set is acquired.
U.S. Pat. No. 6,484,048 discloses a method for enabling an image representation via a suitable interface in the form of a monitor, wherein reference images again are involved in the framework of the image processing.
None of these known methods allows an exact, optimal determination of the image plane in which images for monitoring of the arrival of a contrast agent bolus have to be acquired in order to be able to exactly determine the point in time of the arrival.